1. Field of the Invention
The present invention is related to a noise tolerant temperature sensing circuit which is designed for high speed integrated circuits. More particularly, the present invention provides a temperature sensing circuit that is virtually insensitive to noise in either an analog or digital mode of operation and which provides a very high sensitivity for monitoring temperature or creating critical threshold switching points.
2. Description of the Prior Art
Heretofore, temperature sensing circuits have been placed on integrated circuits. These circuits typically consist of single thermal diodes, zener-diodes, temperature sensing transistors or resistors, all of which are sensitive to noise. In large integration circuits such as gate arrays the noise is so great that accurate temperature sensing can only be accomplished in an inactive state. Any attempt to sense temperature in an active state employing single ended (single output) temperature sensors is virtually impossible.
Typical of such single ended devices are thermal diodes placed on Unisys Corporation A-16 mainframe computer gate arrays used to test individual semiconductor devices at the component state before being incorporated into mainframe computers.
U.S. Pat. No. 4,924,212 shows and describes a temperature sensor which may be incorporated into a VLSI MOS chip to be used in an idle state test. This sensor comprises a reverse saturation stack of two transistors coupled to a voltage threshold comparator circuit.
U.S. Pat. No. 4,970,497 shows and describes a stack of MOS transistors greater than two which are employed as a resistor stack having a voltage output proportional to the temperature being sensed.
U.S. Pat. No. 4,733,162 shows and describes a single ended temperature sensor comprising a multiple emitter transistor that generates an output current which is proportional to temperature.
All of the above prior art circuits are sensitive to noise and as such would not be operable to sense the temperature of a VSLI chip during an on-line operation of a mainframe computer thus, are incapable of being monitored in an active state to determine trouble before a failure. Such circuits would not be useable for on-line computing operations to detect abnormal die temperature conditions and provide a warning before degradation or damage occurs.
It would be desirable to provide an on-chip temperature sensing circuit for high-speed VLSI chips which is capable of producing analog and/or digital signals to drive an off chip maintenance and monitoring device so as to detect problems before they arise and permit proper maintenance operation.